So washed everything (no soap), filled the tank with Arrowhead spring water, added water conditioner, setup the heater/filter and let it run for a day before adding fish #1.

So fish #1 from petco; I put his cup ontop of the water to adjust the to the water temp (81 degress) for an hour, then added him in. He seemed to like it, was active that whole day. But the next morning, he was in serious bad shape, looked like he could barely move, and was dead about 24 hours after going into the tank.

I figured I got a sick/old betta, cleaned out the tank really well, replaced the water, and got another...

So fish #2 from petco; I did the same adjustment thing, and added him. Again, he liked the tank, and was really active, and ate. He was fine for 4 days, but on day 5 he turned super lethargic, and died the next day :(

So am I just having bad luck with petco fish, or is there something I'm doing wrong? Thanks!

How often do you change the water a week? What are you feeding your fish? Also bottled water isn't good, condition tap water from your sink, it has the minerals fish need. Bottled water is over purified to the point it's actually crap. Also more than one plant would be beneficial to your betta. Did you clean the tank between getting the two fish?

I would use your tap water along with the proper amount of dechlorinater instead of bottled water in your tanks-since the bottled water will often be void of the needed minerals.

When you acclimate it is important to acclimate to both temp and chemistry by adding small amount of your dechlorinated tank water to their holding cups over 10-20min or to tolerance.

When you first get your Betta-dump half the water out of the temporary cup they came in and add small amount of your dechlorinated water from the tank. When full-dump half that water out and repeat-then add the Betta without any of the water in the holding cup.....

Or you could have bought sick/weak Betta to start with....But try acclimating them to the new chemistry and see if that will help....

I would use your tap water along with the proper amount of dechlorinater instead of bottled water in your tanks-since the bottled water will often be void of the needed minerals.

When you acclimate it is important to acclimate to both temp and chemistry by adding small amount of your dechlorinated tank water to their holding cups over 10-20min or to tolerance.

When you first get your Betta-dump half the water out of the temporary cup they came in and add small amount of your dechlorinated water from the tank. When full-dump half that water out and repeat-then add the Betta without any of the water in the holding cup.....

Or you could have bought sick/weak Betta to start with....But try acclimating them to the new chemistry and see if that will help....

Look forward to hearing about you new Bettas and seeing pic too.....

Wow, so that is the answer, my friend had the same issue, and was also using Bottled water, and without conditioner, because she was under the impression it would be safer, I had a feeling, but I told her to use Water conditioner, and her betta passed in about 3-4 days as well.

No that seems more like it died from the bottled water. So long as you add water conditioner to your tap water it will be fish safe. It removes everything you don't want but leaves the minerals fish need.

Thanks for the responses! The reason I didn't use tap was because our house has a water softner system, and even after searching around I wasen't sure if that was safe or not.

If you don't have a hard tap inside the house, fill up from a hose bib outside. They shouldn't be tied into the softener, unless it was a quick addition. Either way, the hose bib on your water service will be fine to use.

If the water softening unit on the house uses salt-It is a good idea to bypass it for the water to use with the Betta.

We don't have good regulations on bottled water and sometimes that bottled water is just filtered tap water that can still contain the additives like chlorine/chloramines-Plus the filtering process can remove the needed minerals or it might be an ION exchanger that uses salt-both being bad for fish long term health. Not to mention it can get pretty expensive to use the bottled water-especially when you need to make twice weekly water changes.....
Distilled water is even worse and not just void of minerals but oxygen too.